This invention relates to wafer and die level diagnostic tools to probe micro electromechanical (MEMS) devices during manufacturing processing.
In manufacturing of mechanical assemblies it is advantageous to measure characteristics of a part during intermediate stages of processing. Particularly in the case of micro electromechanical (MEMS) devices, which are batch fabricated using semiconductor processing techniques, it is desirable evaluate the performance of devices early to avoid the expense of further processing a defective wafer. However, since the full functioning of the part often cannot be exercised before the latter stages of fabrication, techniques are needed which can evaluate partial functioning or indirectly assess product quality earlier in the process, and at the wafer level. Such diagnostics are a valuable part of process engineering to enhance yields and reduce scrap, cost and cycle time.
Many such diagnostic tools exist for semiconductor processes, however because of the relative novelty and variety of MEMS materials and devices, few tools have been developed which can evaluate the devices in situ. If the MEMS device is an electrostatic actuator for example, the device must be free to move, and vias need to be provided to electrical contacts in order to induce motion. Often, however, the circuit is not sufficiently complete until the latter steps of fabrication. A shaker table may be used to impart relative motion to the device in the absence of a driving circuit, however MEMS are generally low inertia devices, with high surface area-to-mass ratios and high stiffness. Therefore in order to effect large deflections in the devices, high amplitude vibration may be required which can be damaging to the product.
Therefore, there exists an ongoing need in the MEMS art, for simple, non-destructive diagnostic tools for wafer level probing of micromechanical devices.